Average Weather in Union South Carolina, United States

In Union, the summers are hot and muggy, the winters are cold and wet, and it is partly cloudy year round. Over the course of the year, the temperature typically varies from 35°F to 90°F and is rarely below 23°F or above 97°F.

Based on the tourism score, the best times of year to visit Union for warm-weather activities are from early May to early June and from late August to mid October.

Temperature

The hot season lasts for 3.6 months, from May 26 to September 14, with an average daily high temperature above 83°F. The hottest day of the year is July 21, with an average high of 90°F and low of 71°F.

The cool season lasts for 3.0 months, from November 27 to February 27, with an average daily high temperature below 60°F. The coldest day of the year is January 17, with an average low of 35°F and high of 52°F.

The daily average high (red line) and low (blue line) temperature, with 25th to 75th and 10th to 90th percentile bands. The thin dotted lines are the corresponding average perceived temperatures.

The figure below shows you a compact characterization of the entire year of hourly average temperatures. The horizontal axis is the day of the year, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.

Clouds

In Union, the average percentage of the sky covered by clouds experiences mild seasonal variation over the course of the year.

The clearer part of the year in Union begins around August 2 and lasts for 3.8 months, ending around November 26. On October 8, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy66% of the time, and overcast or mostly cloudy34% of the time.

The cloudier part of the year begins around November 26 and lasts for 8.2 months, ending around August 2. On January 4, the cloudiest day of the year, the sky is overcast or mostly cloudy51% of the time, and clear, mostly clear, or partly cloudy49% of the time.

The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds.

Precipitation

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Union varies throughout the year.

The wetter season lasts 3.2 months, from May 24 to August 29, with a greater than 32% chance of a given day being a wet day. The chance of a wet day peaks at 45% on August 5.

The drier season lasts 8.8 months, from August 29 to May 24. The smallest chance of a wet day is 19% on October 29.

Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 45% on August 5.

Daily Chance of Precipitation

The percentage of days in which various types of precipitation are observed, excluding trace quantities: rain alone, snow alone, and mixed (both rain and snow fell in the same day).

Rainfall

To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. Union experiences some seasonal variation in monthly rainfall.

Rain falls throughout the year in Union. The most rain falls during the 31 days centered around March 2, with an average total accumulation of 3.8 inches.

The least rain falls around October 31, with an average total accumulation of 2.8 inches.

The average rainfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average liquid-equivalent snowfall.

Snowfall

The sliding 31-day liquid-equivalent quantity of snowfall in Union does not vary significantly over the course of the year, staying within 0.1 inches of 0.1 inches throughout.

The average liquid-equivalent snowfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average rainfall.

Sun

The length of the day in Union varies significantly over the course of the year. In 2018, the shortest day is December 21, with 9 hours, 50 minutes of daylight; the longest day is June 21, with 14 hours, 29 minutes of daylight.

The number of hours during which the Sun is visible (black line). From bottom (most yellow) to top (most gray), the color bands indicate: full daylight, twilight (civil, nautical, and astronomical), and full night.

The earliest sunrise is at 6:12 AM on June 12, and the latest sunrise is 1 hour, 36 minutes later at 7:48 AM on November 3. The earliest sunset is at 5:15 PM on December 5, and the latest sunset is 3 hours, 28 minutes later at 8:43 PM on June 29.

Daylight saving time (DST) is observed in Union during 2018, starting in the spring on March 11, lasting 7.8 months, and ending in the fall on November 4.

The solar day over the course of the year 2018. From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray. The transitions to and from daylight saving time are indicated by the 'DST' labels.

Humidity

We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.

The muggier period of the year lasts for 4.6 months, from May 15 to October 3, during which time the comfort level is muggy, oppressive, or miserable at least 22% of the time. The muggiest day of the year is July 24, with muggy conditions 89% of the time.

The least muggy day of the year is February 9, when muggy conditions are essentially unheard of.

The percentage of time spent at various humidity comfort levels, categorized by dew point.

Wind

This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.

The average hourly wind speed in Union experiences mild seasonal variation over the course of the year.

The windier part of the year lasts for 7.4 months, from October 6 to May 18, with average wind speeds of more than 4.7 miles per hour. The windiest day of the year is March 8, with an average hourly wind speed of 5.7 miles per hour.

The calmer time of year lasts for 4.6 months, from May 18 to October 6. The calmest day of the year is August 1, with an average hourly wind speed of 3.7 miles per hour.

The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.

The predominant average hourly wind direction in Union varies throughout the year.

The wind is most often from the north for 1.3 months, from February 6 to March 16 and for 3.5 months, from September 15 to December 29, with a peak percentage of 36% on October 15. The wind is most often from the west for 4.0 months, from April 10 to August 10 and for 1.2 months, from December 29 to February 6, with a peak percentage of 36% on July 5. The wind is most often from the east for 1.2 months, from August 10 to September 15, with a peak percentage of 34% on September 6.

Wind Direction

The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions, excluding hours in which the mean wind speed is less than 1.0 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

Best Time of Year to Visit

To characterize how pleasant the weather is in Union throughout the year, we compute two travel scores.

The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best times of year to visit Union for general outdoor tourist activities are from early May to early June and from late August to mid October, with a peak score in the third week of September.

The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best time of year to visit Union for hot-weather activities is from early June to mid September, with a peak score in the third week of August.

Methodology

For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.

Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.

Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.

Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.

Growing Season

Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).

The growing season in Union typically lasts for 7.7 months (236 days), from around March 22 to around November 13, rarely starting before March 2 or after April 10, and rarely ending before October 26 or after December 1.

The percentage of time spent in various temperature bands. The black line is the percentage chance that a given day is within the growing season.

Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.

Based on growing degree days alone, the first spring blooms in Union should appear around February 14, only rarely appearing before January 27 or after March 4.

Growing Degree Days

The average growing degree days accumulated over the course of the year, with 25th to 75th and 10th to 90th percentile bands.

Solar Energy

This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.

The average daily incident shortwave solar energy experiences significant seasonal variation over the course of the year.

The brighter period of the year lasts for 4.4 months, from April 13 to August 24, with an average daily incident shortwave energy per square meter above 6.0 kWh. The brightest day of the year is June 23, with an average of 6.8 kWh.

The darker period of the year lasts for 2.9 months, from November 11 to February 6, with an average daily incident shortwave energy per square meter below 3.4 kWh. The darkest day of the year is December 25, with an average of 2.5 kWh.

The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.

Topography

For the purposes of this report, the geographical coordinates of Union are 34.715 deg latitude, -81.624 deg longitude, and 561 ft elevation.

The topography within 2 miles of Union contains only modest variations in elevation, with a maximum elevation change of 213 feet and an average elevation above sea level of 573 feet. Within 10 miles also contains only modest variations in elevation (423 feet). Within 50 miles contains only modest variations in elevation (3,058 feet).

The area within 2 miles of Union is covered by trees (47%), artificial surfaces (42%), and cropland (10%), within 10 miles by trees (84%) and cropland (14%), and within 50 miles by trees (69%) and cropland (19%).

Data Sources

This report illustrates the typical weather in Union, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.

Temperature and Dew Point

There are 6 weather stations near enough to contribute to our estimation of the temperature and dew point in Union.

The estimated value at Union is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Union and a given station.

Other Data

All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.

Disclaimer

The information on this site is provided as is, without any assurances as to its accuracy or suitability for any purpose. Weather data is prone to errors, outages, and other defects. We assume no responsibility for any decisions made on the basis of the content presented on this site.

We draw particular cautious attention to our reliance on the MERRA-2 model-based reconstructions for a number of important data series. While having the tremendous advantages of temporal and spatial completeness, these reconstructions: (1) are based on computer models that may have model-based errors, (2) are coarsely sampled on a 50 km grid and are therefore unable to reconstruct the local variations of many microclimates, and (3) have particular difficulty with the weather in some coastal areas, especially small islands.

We further caution that our travel scores are only as good as the data that underpin them, that weather conditions at any given location and time are unpredictable and variable, and that the definition of the scores reflects a particular set of preferences that may not agree with those of any particular reader.